Environmental Protection Agency Administrator Scott Pruitt has caught flak for flying first class, paying just $50 per night for a Capitol Hill rental and reportedly shuffling staffers who questioned his spending.

The Office of Government Ethics in a new letter warned the EPA that Pruitt's actions "raise concerns and may constitute a violation" of federal ethics rules.

Pruitt's large security detail, which costs millions of dollars, is justified by the number of death threats he has received, according to the EPA.

The letter sent Friday and made public Monday laid out what has become a litany of controversies surrounding Pruitt, whose hold on his job as EPA administrator has become tenuous. The EPA had no immediate comment.

It was revealed recently that Pruitt last year rented a room in Washington for just $50 per night from Vicki Hart, wife of lobbyist Steven Hart, whose clients were seeking action from the EPA. The agency's ethics official, Kevin Minoli, last week said that his initial determination that the rental deal did not violate federal rules was based on incomplete facts about that arrangement.

David Apol, acting director and general counsel of the Office of Government Ethics, in his letter to Minoli said the reported actions of Pruitt "raise concerns and may constitute a violation of the Standards of Ethical Conduct for Employees of the Executive Branch."

Apol wrote that "our understanding" is that Pruitt "apparently did not seek ethics advice prior to entering into the lease" with Vicki Hart on the question of whether the lease's terms "were so favorable as to be a gift from the lobbyist."

"Only after the existence of the lease was reported in the press did he provide EPA ethics advisors with limited information about the lease," Apol wrote. "He then received, based on the incomplete information he provided, an after-the-fact opinion that the lease did not constitute a gift."

"Additional information has now come to light that calls into question whether the earlier determination that the Administrator paid market value for the use he made of the apartment would still be valid," Apol wrote.

The ethics official wrote that while "appropriate use of scarce government resources is beyond the purview of OGE," reports about Pruitt making frequent official trips to his home state of Oklahoma "to offset the expense of returning home for personal and political reasons" raise concerns about whether he is using his office "for personal gain in violation of ethics rules."

"Finally, there are extremely concerning reports that the Administrator has reassigned or demoted staff who were attempting to ensure that the expenses and other actions were in accordance with laws and regulations," Apol wrote.

"If true, it is hard to imagine any action that could more effectively undermine an agency's integrity than punishing or marginalizing employees who strive to ensure compliance with the laws and regulations that safeguard that integrity."

Apol said OGE "expects that the EPA will review and analyze the alleged conduct."

He noted that the EPA's Office of Inspector General is already reviewing requests to probe at least some of the issues.

"If a violation is found, OGE expects that appropriate action will be taken in response," Apol wrote.